Merge branch 'jc/test-must-be-empty' into next

Test helper update.

* jc/test-must-be-empty:
  test_must_be_empty: simplify file existence check

Author: gitster

t/test-lib-functions.sh

@@ -782,11 +782,8 @@ verbose () {
 # otherwise.
 
 test_must_be_empty () {
-	if ! test -f "$1"
-	then
-		echo "'$1' is missing"
-		return 1
-	elif test -s "$1"
+	test_path_is_file "$1" &&
+	if test -s "$1"
 	then
 		echo "'$1' is not empty, it contains:"
 		cat "$1"